Susceptibility of atrazine photo-degradation in the presence of nitrate: Impact of wavelengths and significant role of reactive nitrogen species

Journal Pre-proof Dionysios D. Dionysiou: Funding acquisition; Writing - review and editing.Susceptibility of atrazine photo-degradation in the presence of nitrate: Impact of wavelengths and significant role of reactive nitrogen species Lingjun Bu (Conceptualization) (Data curation) (Software) (Validation) (Writing - original draft), Ningyuan Zhu (Conceptualization) (Writing - original draft), Chunquan Li (Investigation) (Visualization), Ying Huang (Conceptualization), Minghao Kong (Formal analysis) (Writing - review and editing), Xiaodi Duan (Methodology) (Project administration) (Supervision) (Writing - review and editing), Dionysios D. Dionysiou (Funding acquisition) (Writing - review and editing)

PII:

S0304-3894(19)31714-5

DOI:

https://doi.org/10.1016/j.jhazmat.2019.121760

Reference:

HAZMAT 121760

To appear in:

Journal of Hazardous Materials

Received Date:

9 October 2019

Revised Date:

20 November 2019

Accepted Date:

25 November 2019

Please cite this article as: Bu L, Zhu N, Li C, Huang Y, Kong M, Duan X, Dionysiou DD, Dionysios D. Dionysiou: Funding acquisition; Writing - review and editing.Susceptibility of atrazine photo-degradation in the presence of nitrate: Impact of wavelengths and significant role of reactive nitrogen species, Journal of Hazardous Materials (2019), doi: https://doi.org/10.1016/j.jhazmat.2019.121760

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.

Susceptibility of atrazine photo-degradation in the presence of nitrate: Impact of wavelengths and significant role of reactive nitrogen species

Lingjun Bua, b, 1, Ningyuan Zhub, c, 1, Chunquan Lib, d, Ying Huangb, Minghao Kongb,

a

ro of

Xiaodi Duanb, *, Dionysios D. Dionysioub

Key Laboratory of Building Safety and Energy Efficiency, Ministry of Education,

-p

Department of Water Engineering and Science, College of Civil Engineering, Hunan University, Changsha, 410082, China

Department of Chemical and Environmental Engineering, 705 Engineering Research

re

b

Center, University of Cincinnati, Cincinnati, OH 45221-0012, USA c

lP

Zigui Ecological Station for Three Gorges Dam Project, State Key Laboratory of Soil

and Sustainable Agriculture, Institute of Soil Sciences, Chinese Academy of Sciences,

d

na

71 East Beijing Road, Nanjing 210008, China

School of Chemical and Environmental Engineering, China University of Mining and

Jo

ur

Technology (Beijing), Beijing 100083, PR China

*

Corresponding author: Xiaodi Duan ([email protected])

1

These authors contributed equally to this work and shared co-first authorship.

Graphical absctract



ro of -p

Highlights



RNS are major contributor to degradation of ATZ in UV285/nitrate.



RNS are helpful to accelerate the photo-transformation of ATZ.

lP

na

Abstract

re



The influence of UV light wavelengths on degradation of ATZ was investigated. UV285/nitrate showed better performance than UV255/nitrate.

ur

The role of reactive nitrogen species (RNS) formed from nitrate photolysis has aroused interests in transformation of contaminants of emerging concern. This study

Jo

investigated the influence of UV wavelengths (255, 285 and 365 nm) on photolysis of nitrate for degradation of atrazine (ATZ). The UV285/nitrate system showed the fastest rate constant for degradation of ATZ with kobs of 0.0022 cm2 mJ-1. UV photolysis, RNS, and hydroxyl radical (HO•) were identified as main contributors to ATZ degradation in UV/nitrate system. Among the contributors, RNS made the major contribution to degradation of ATZ in UV285/nitrate system, while HO• is the predominant specie in

UV255/nitrate system. Variance decomposition analysis showed that degradation of ATZ was slightly impacted by natural organic matter and carbonate/bicarbonate in UV285/nitrate system but was dramatically affected in UV255/nitrate system. Main transformation products of ATZ in UV285/nitrate system were identified and possible pathways were proposed. RNS were confirmed to be favorable for acceleration of ATZ photolysis through further reaction of RNS with hydroxyatrazine (with electron-rich moieties). Our study provides deep insights on the influence of UV wavelength on

ro of

nitrate photolysis and ATZ degradation, and provides a novel method for remediation of water co-contaminated by nitrate and organic contaminants.

re

-p

Keywords: UV wavelength; nitrate photolysis; atrazine; reactive nitrogen species.

lP

1. Introduction

Nitrate (NO3−) photolysis has received great attention in past decades because the

na

ubiquitous NO3− is a main source of reactive radicals in natural waters in the presence of solar light [1]. Although the nitrate photolysis may pose health risks in water

ur

purification because of the formation of nitro-derived compounds [2], researchers has proven the important role of photolyzed nitrate in the degradation of contaminants of

Jo

emerging concern (CECs) [3-5]. Photolysis of nitrate could produce hydroxyl radicals (HO•) and reactive nitrogen species (RNS) (Eqs. 1-4), such as nitrogen dioxide radical (NO2•), nitrite (NO2−), O(3P), and peroxynitrite (ONOO−) [6-9]. The photolyzed pathways of nitrate have been intensively and thoroughly investigated at different light wavelengths [9, 10]. However, the impact of light wavelengths on nitrate photolysis associated with degradation of contaminant has not been previously investigated in

depth. NO3− + hv → NO2• + O•−

(1)

O•− + H2O → HO• + OH−

(2)

NO3− + hv → NO2− + O(3P)

(3)

NO2• + HO• → HOONO

(4)

NO2− + HO• → NO2• + OH−

(5)

ro of

Among the products of photolyzed nitrate, HO• and RNS have been confirmed to

possess the potential to attack CECs [3, 5]. The quantum yields of HO• from nitrate photolysis was reported to be higher at short wavelengths: around 9% at UV254, and

-p

declined steadily to 1% with the wavelength increasing to 300 nm and above [9, 11]. However, the generated HO• (E0 = 2.0 V) [12] could be quenched by other products of

re

photolyzed nitrate, such as nitrite or NO2• (Eqs 4-5) [9], and usually be quenched by

lP

carbonate/bicarbonate ions and organic matters, limiting the reactions between HO• and target contaminants [13]. Taking NO2• (E0 = 1.03 V) [14] as an example, RNS are

[3, 15].

na

usually selective and can react rapidly with contaminants with electron-rich moieties

ur

Atrazine (ATZ), as one of the triazine herbicides, has received much attention because of the continually increasing consumption in agriculture field and the

Jo

potentially toxic impacts when leaching into aquatic ecosystems [16, 17]. Former research studies showed that photo-transformation of ATZ was an important pathway for ATZ removal, which was hardly affected by the wavelength of light source [18]. However, direct photolysis of ATZ is inadequate because the main intermediate products (hydroxyatrazine and 4-ethylamino-6-isopropylamino-2-hydroxy-s-triazine) are inert for further photolysis [19]. Notably, ATZ and nitrate are simultaneously

present in agricultural runoffs which causes widely pollution in surface waters [20, 21]. Therefore, the generated HO• and RNS from the photolysis of nitrate (eqs. 1-5) can efficiently degrade the co-existed ATZ, and RNS mainly remove ATZ via electrophilic substitution. Nitrate often exists in agricultural runoffs at concentrations up to 0.6 mM [13]. Only few research studies have focused on the photochemical removal of ATZ in the presence of nitrate [3, 19], especially on the role of RNS because of the electrondonated nature of ATZ. Also, investigations on the degradation of ATZ using different

ro of

light wavelengths in the presence of nitrate can provide new insights for remediation of ATZ-polluted water.

Thus, this study aims to 1) investigate the impact of light wavelength on nitrate

-p

photolysis for ATZ degradation; 2) evaluate the contributions of RNS on ATZ

degradation in the presence of nitrate.

2.1 Photolysis experiments

lP

2. Materials and Methods

re

degradation and 3) explore the possible degradation mechanisms involved during ATZ

na

Photolysis experiments were carried out with collimated UV-LEDs (255 nm, 0.03 mW cm−2; 285 nm, 0.12 mW cm−2; and 365 nm, 3.05 mW cm−2, Pearlbeam, AquiSense

ur

Technologies, KY) in a laboratory scale system. The UV intensity was determined by

Jo

ferrioxalate actinometry method reported in our previous study [22]. In a typical experiment, solutions were prepared with 1 μM of ATZ and 4 mM nitrate with a total volume of 10 mL in a petri dish (60 × 15 mm) with a quartz cover (Quartz Scientific Inc., OH), unless stated otherwise. All experiments were performed in triplicates at ambient temperatures (21 ± 1 °C). The reaction was initiated by collimated UV-LEDs illumination of individual of beam. At different time intervals, 200 μL of solution

samples were collected and quenched by 50 μL methanol (MeOH) for further analysis. After reaction, the samples were taken to analyze the concentration of nitrate and nitrite. All chemicals used in this study were of analytical grade purity and were obtained from Sigma-Aldrich. In another set of experiments, direct ATZ photolysis was detected in the same reactor with the same light conditions as above mentioned. The solution only composed of 10 mL of ATZ with the concentration of 1 μM.

ro of

To evaluate the ATZ degradation performance in natural water, filtered water

samples were collected from Lao Yinggou River (Yichang, Hubei). Experiments were carried out as the same procedures mentioned above in collected water samples with

-p

spiked chemicals. To distinguish the influence of initial concentration of nitrate, initial

re

pH, natural organic matters (NOM) and bicarbonate/carbonate on ATZ degradation by nitrate photolysis, experiments were conducted with the same conditions mentioned

lP

above. To explore the influence of initial concentration of nitrate, ATZ was also treated at the nitrate concentration ranging from 0 to 10 mM (0, 0.2, 2, 4, 6, 10 mM). Besides,

na

to evaluate the influence of pH, experiments were carried out at pH ranging from 4.0 to 8.5 which was adjusted by 0.05 M H2SO4 or 0.1 M NaOH. Different dosages of NOM

ur

(from Suwannee River, supplied by international humic substances society, 0-10 mg-C L-1) and NaHCO3 (0, 50, 100, 150, 200 mg L-1) were added to the reactor, respectively,

Jo

to investigate the influence of NOM and alkalinity. 2.2 Contributions of reactive species In UV/nitrate system, direct UV photolysis, oxidation by HO• or RNS could result in the degradation of ATZ as follow: −

d[ATZ] dt

= Li × k photolysis [ATZ] + k HO•ATZ [HO• ][ATZ] + k RNS,ATZ [RNS][ATZ] (6)

where Li is the light intensity, kphotolysis represents the reaction rate calculated from ATZ degradation by direct UV irradiation, kHO•,ATZ and kRNS,ATZ are the second-order rate constants of ATZ with HO• and RNS, respectively. The steady-state concentration of HO• ([HO•]ss) was then estimated because the concentration of nitrate changed slightly before and after reaction according to Huang et al.’s method [3]. Nitrobenzene (NB), an effective hydroxyl radical scavenger with known rate constants [22], was selected as the HO• probe because of the negligible degradation by RNS. The degradation of 50

ro of

μM of NB by direct UV photolysis and UV/nitrate at different wavelengths were measured by HPLC. Thus, the [HO•]ss was then calculated following Eq. (8): d[NB] dt

= Li × k photolysis [NB] + k HO• ,NB [HO• ]ss [NB] = k obs [NB]

(7)

-p

−

where the Li is the light intensity, kphotolysis represents the reaction rate of direct UV

re

degradation of NB, k HO• ,NB (the second-order rate constant of NB with HO•) is 3.9 × 109 M-1 s-1 [12]. The degradation curves of NB by UV255/nitrate, UV255 irradiation,

lP

UV285/nitrate, UV285 irradiation are presented in Figure S1. The [HO•]ss was calculated after knowing the value for kphotolysis related to NB degradation (Table S1). Then, the

R= 𝑡

𝑡

ur

as follows:

na

contribution of UV photolysis, HO• and RNS on ATZ degradation could be calculated

[𝐴𝑇𝑍]0 −[𝐴𝑇𝑍]𝑡 𝐴𝑇𝑍0

=

∫0 𝑘𝑝ℎ𝑜𝑡𝑜𝑙𝑦𝑠𝑖𝑠 [𝐴𝑇𝑍]𝑑𝑡

Jo

∫0 kRNS,ATZ [𝑅𝑁𝑆][𝐴𝑇𝑍]𝑑𝑡 𝐴𝑇𝑍0

𝐴𝑇𝑍0

𝑡

+

∫0 kHO• ATZ [𝐻𝑂• ][𝐴𝑇𝑍]𝑑𝑡 𝐴𝑇𝑍0

+

= 𝑅𝑝ℎ𝑜𝑡𝑜𝑙𝑦𝑠𝑖𝑠 + 𝑅𝐻𝑂• +𝑅𝑅𝑁𝑆

(8)

where R is the removal of ATZ from different contributors, [ATZ]0 is the initial

concentration of ATZ, and [ATZ]t is the concentration of ATZ at a given time t. The detailed information about the calculation is presented in Table 1. 2.3 Analytical methods and statistics

The concentration of ATZ was determined by High Performance Liquid Chromatography (HPLC, Agilent1100 Series). The Agilent 1260 infinity HPLC, equipped with an Eclipse XDB-C18 column (2.1 mm × 50 mm × 3.5 μm, Agilent ZORBAX), with an Agilent 6420 triple quadrupole mass spectrometer (LC-MS) was used to analyze the transformation products of ATZ. Mass spectra were analyzed by Agilent Mass Hunter B.04.00 software. The variation of toxicity during the treatment was experimentally monitored using bacterial luminescence Vibrio fischeri (strain Nitrate

and

nitrite

concentrations

were

determined

ro of

NRRL-B-11177).

spectrophotometrically based on Brucine-sulfanil colorimetric method [23] and Griess

Assay reaction [24], respectively, using a double UV-vis Spectrophotometer (UV-2450

-p

Shimadzu, Japan) [25].

Variance partition analysis (VPA) was performed to distinguish the role of

re

different natural components (concentration of nitrate, dissolved organic carbon, pH,

lP

carbonate/bicarbonate) on ATZ degradation by UV/nitrate at different wavelengths. These analyses were performed using R software with vegan package (the detailed

na

running script was supplied in SI Text S1). One-way AVONA was used for statistical analysis and the probability value was set at 0.05 level for all analyses.

ur

3. Results and Discussion

Jo

3.1 Degradation of ATZ by photolysis of nitrate The degradation of ATZ (1 μM) by UV-LEDs with different radiation wavelengths

(255, 285 and 365 nm) in the presence of nitrate was investigated in a series of experiments. As shown in Figure 1a, 87.7% of ATZ was removed after 120 min irradiation by UV285 whereas UV255 and UV365 eliminated no more than 12% ATZ in the presence of nitrate. The time-based pseudo-first order rate constants (ktobs) of ATZ

degradation were 0.0008 min-1, 0.0158 min-1, 0.0005 min-1 for UV255, 285 and 365 nm, respectively (Figure S2). The UV fluence based pseudo-first order rate constants (kfobs) were then calculated in consideration of the influence of intensities [26]. The kfobs for UV285 was 0.0022 cm2 mJ−1 which was 7.3 times compared to that of UV255 in the presence of nitrate. UV365 was not studied in the following sections because the kfobs for UV365 (0.0002 cm2 mJ−1) was much lower than that of UV285. Meanwhile, direct photolysis of ATZ in the absence of nitrate was also considered: UV285 showed a better

ro of

performance on the degradation of ATZ than UV255 in sole photolysis process (Figure S3), suggesting that UVB (285 nm) irradiation was more effective to decompose ATZ in the absence or presence of nitrate. Of note, the UV adsorption spectrum of nitrate

-p

has two peaks at ~200 nm band (190 to 250 nm) and ~300 nm band (270 to 330 nm),

respectively [9, 10]. As known, the wavelength of solar light reaching down to the

re

terrestrial surface waters is above 290 nm [27]. Thus, this study shows the feasibility of

lP

nitrate responses to ~300 nm band irradiation for transformation of organic contaminants. We also investigated ATZ degradation by photolysis of nitrate under UVvis light (300-760 nm), which also resulted in 35.3% ATZ removal (Figure S4). Among

na

the photolysis products of nitrate, the HO• and RNS (mainly NO• and N2O•) could result in degradation of organic contaminants [3]. As referred above, the quantum yield of

ur

HO• from nitrate photolysis at UV255 is much higher than that of UV285 [8, 28]. However,

Jo

this study showed a much more effective degradation for ATZ at UV285 than UV255, indicating that RNS play an important role in ATZ degradation. 3.2 Contribution of reactive species on ATZ degradation ATZ could be degraded by direct UV photolysis and reactive radicals such as HO• and RNS generated from photolysis of nitrate [9, 19]. To distinguish the respective contributions of UV photolysis, HO• and RNS on ATZ degradation in UV/nitrate system,

calculations were carried out according to the methods reported by Fang et al. [29, 30], which is shown in Table 1. There were approximately 26.0% and 86.0% of ATZ degraded by UV255/nitrate and UV285/nitrate systems, respectively, at UV fluence of 864 mJ cm-2. Direct UV photolysis (in the absence of nitrate) removed 4.0% and 12.0% of ATZ at UV255 and UV285, respectively, based on the calculated results (Figure 2A and B). As calculated, 14.5% of ATZ was removed by HO• oxidation under UV255/nitrate while only 1.0% of ATZ was removed by UV285/nitrate (Figure 2A and B).

ro of

Correspondingly, the contribution of HO• to ATZ degradation was considerably high (55.8%) for UV255/nitrate but low (1.2%) for UV285/nitrate at UV fluence of 864 mJ cm2

(Figure 2C). On the other hand, only 28.6% of ATZ degradation was attributed to RNS

-p

in UV255/nitrate system while RNS contributed 84.9% to ATZ degradation in UV285/nitrate system (Figure 2C).

re

Former studies also observed the formation of 2-hydroxyatrazine by direct

lP

photolysis of ATZ at shorter wavelengths (254-290 nm) [19, 31]. The formed 2hydroxyatrazine was too stable to be further decomposed [32], resulting in a low ATZ

na

removal efficiency through UV photolysis. Photolysis of nitrate could also generate HO•, the amount of which decreased steadily with the wavelength increasing from 254

ur

nm to 300 nm (e.g. a quantum yield of 9% at UV254 and around 1% at UV300) [7, 9]. The calculated steady-state concentrations of HO• were 5.5 × 10-15 M and 1.2 × 10M for UV255 and UV285, respectively. Thus, the degradation of ATZ by HO• oxidation

Jo

15

at UV285 was much lower than that of UV255. Still, the ATZ removal efficiency was considerably low in UV255/nitrate system compared to the sulfate radical based advanced oxidation process (AOPs) deriving from activation of sulfite [33] or peroxymonosulfate [34] and electrochemical activation of persulfate [35]. This may be due to that the reaction rate constant of ATZ with HO• (3.0 × 109 M-1s-1) is relatively

lower than that with sulfate radicals (4.2 × 109 M-1s-1). The role of RNS has shown to be important in degradation of contaminants with phenolic structure because of the presence of electron-rich moieties [3-5], while the electron-donated moieties of ATZ made it less susceptible to RNS. Interestingly, the photolyzed products of ATZ, 2-hydroxyatrazine, has electron-rich moieties which further facilitates attack by RNS. Considering the generated transformation products, higher yield of RNS in UV285/nitrate could be beneficial to the degradation of

ro of

contaminants compared to UV255/nitrate process. Figure S3 also shows more ATZ was removed through direct UV photolysis at 285 nm than that at 255 nm. However, the contribution from UV photolysis to ATZ degradation was not significantly different

re

3.3 ATZ degradation in authentic waters

-p

between the UV255/nitrate and UV285/nitrate processes (Figure 2A and B).

Nitrate is ubiquitous in natural waters in the range from 0.01 to 1 mM [9]. In this

lP

study, field water samples were collected from Lao Yinggou River (Yichang, China) on Mar 26th, May 28th, Jun 27th and Jul 19th. The nitrate concentration in this river could

na

reach to 1 mM because of the overuse of fertilizer [36]. The removal efficiency of ATZ ranged from 0.7% to 12.4% for UV255 at 864 mJ cm-2 UV fluence while ATZ decreased

ur

by 6.3% to 44.9% for UV285 (Table S2). The results further confirmed that UV285 is

Jo

more suitable to be used as light source in practical applications. VPA analysis was then used to distinguish the role of environmental factors (initial

concentration of nitrate, NOM, and carbonate/bicarbonate + pH) on ATZ degradation. In UV255/nitrate system, ATZ degradation was mainly dependent on the interaction between NOM and nitrate, which made the primary influence on ATZ removal (60%) (Figure 3A). The nitrate alone accounted for 13% of ATZ degradation while the

interaction between nitrate and carbonate/bicarbonate + pH achieved 12% of ATZ degradation. In UV285/nitrate system, ATZ degradation was mainly ascribed to initial nitrate concentration (64%) while the interaction between NOM and nitrate yielded 25% of ATZ degradation (Figure 3B). NOM or carbonate/bicarbonate served as scavengers of HO• [37, 38], which may affect ATZ removal in UV255/nitrate system. Interestingly, NOM and carbonate/bicarbonate were less prone to scavenge RNS [5, 39]. 3.4 Influence of environmental factors

ro of

Influence of initial nitrate concentration. The photochemical degradation of ATZ (1 μmol) was carried out in the presence of nitrate ranging from 0.2 to 10 mM. The

removal of ATZ under UV255 increased from 15.2% to 45.8% when nitrate

-p

concentration was increased from 0.2 to 10 mM at 864 mJ cm-2 (Figure S5A).

re

Interestingly, the conversion of ATZ under UV285 increased from 38.7% to 90.3% with nitrate concentration increasing from 0.2 mM to 10 mM (Figure S5B). The increase in

lP

initial nitrate concentration result in enhancement of ATZ degradation both for UV255 and UV285, which can be ascribed to the increased steady-state concentrations of HO•

na

and RNS for UV255/nitrate and UV285/nitrate systems [3, 40]. Correspondingly, the kobs increased from 0.0002 cm2 mJ-1 to 0.0007 cm2 mJ-1 and from 0.0005 cm2 mJ-1 to 0.0027

ur

cm2 mJ-1 for UV255 and UV285, respectively (Figure 4A). Thus, the initial concentration of nitrate affected ATZ degradation in UV285/nitrate more dramatically compared to

Jo

UV255/nitrate system, which was consistent to the VPA result. Influence of natural organic matter. The effect of NOM (0 to 10 mg-C L-1) on

ATZ degradation by nitrate photolysis was then investigated. For UV255/nitrate system, ATZ degradation was inhibited when the NOM concentration increased from 0 to 10 mg-C L-1. Higher concentration of NOM (> 1 mg-C L-1) dramatically inhibited ATZ degradation in UV255/nitrate system (Figure S6A). This is because that NOM is a good

scavenger of HO• which results in decrease in reaction between HO• and target contaminants [41, 42]. On the other hand, ATZ degradation was inhibited slightly in the UV285/nitrate system in the presence of NOM of 0-4 mg-C L-1. When NOM concentration further increased to 7 and 10 mg-C L-1, the presence of NOM even promoted the degradation of ATZ (Figure S6B). The phenomenon could be explained by the production of singlet oxygen from photolysis of NOM, irradiated by UV of higher wavelengths [43, 44], which facilitates photochemical degradation of ATZ [45].

ro of

Thus, the interaction between NOM and photogenerated radicals from nitrate photolysis could affect ATZ degradation which is consistent with our VPA results.

Influence of initial pH. The impact of initial pH (4.0, 6.1, 7.2, 8.1 and 9.0) on ATZ

-p

degradation by nitrate photolysis was also studied. Results showed that ATZ degradation under UV255/nitrate was not significantly affected by solution pH (Figure

re

S7A). With the initial pH increasing from 4.0 to 9.0, ATZ degradation under UV285

lP

increased from 59.3% (pH 4.0) to 86.0% (pH 7.2), and then decreased to 83% (pH 9.0) (Figure S7B). Previous studies about nitrate photolysis had demonstrated that acidic

na

solution facilitated HOONO production (Eq. (4)), followed by the regeneration of nitrate (Eq.(10)) [28, 46], which caused the decrease in quantum yield of RNS. Thus,

ur

the kobs for UV285 was 0.0010 cm2 mJ-1 at pH 4.0 which was significantly lower than that at the higher pH values (Figure 4B).

Jo

HOONO → NO3− + H+

(9)

Influence of alkalinity. The influence of bicarbonate/carbonate on ATZ

degradation by nitrate photolysis was then investigated in the range from 0 to 200 mg L-1. The inhibition of ATZ removal increased in UV/nitrate system at different wavelengths with the increase in bicarbonate/carbonate concentration (Figure S8). The phenomenon can be explained from two aspects: (1) solution pH was 7.20, 7.62, 7.93,

8.19, and 8.35 when bicarbonate concentration was 0, 50, 100, 150, and 200 mg/L, respectively, and ATZ removal was inhibited with the increase of pH; (2) the presence of carbonate/bicarbonate ions can react with HO• to produce carbonate radicals (CO3•−) as shown in the following equations [47, 48]: HCO3− + HO• → CO3•− + H2O

(10)

CO32− + HO• → CO3•− + OH−

(11)

ro of

Thus, carbonate/bicarbonate can quench HO• and thus affect ATZ degradation in UV/nitrate system because CO3•− cannot degrade ATZ [3]. Carbonate/bicarbonate also

reacts with nitrogen species derived from nitrate photolysis in alkaline solutions as

-p

follows [49]:

ONOOC(O)O− → CO3•− + NO2•

re

ONOO− + CO2 → ONOOC(O)O−

(12) (13)

lP

On consideration of the low productivity of ONOO− during nitrate photolysis, the influence of carbonate/bicarbonate on RNS was negligible [3, 9].

na

3.5 Transformation products and toxicity variation of ATZ in UV285/ nitrate The role of radiation wavelength at 285 nm was then investigated for the rest of

ur

this study on consideration of the highest degradation efficiency of ATZ in the presence of 10 mM nitrate. The molecular weight and structures of possible transformation

Jo

products were proposed according to the ratio of mass to charge (m/z) and retention time. Based on the products detected, the possible degradation pathways of ATZ in UV285/nitrate system are shown in Figure 5. Because of the simultaneous involvement of direct UV photolysis, HO• and RNS, different reactions (including dechlorinationhydroxylation, amine oxidation and dechlorination) take place in this system. The first route involved dechlorination-hydroxylation reactions via electron transfer. There are

two possible mechanisms for this process to produce OEIT (m/z = 198.185). One was the direct photolysis of ATZ which has been reported in previous studies [18, 19]. The other could be attributed to the reaction between ATZ and NO2• or NO• to obtain an electron and form [C8H14ClN5]•) [50] (Scheme 1). The dechlorinated-hydroxylated intermediate products (C8H15N5O) were then produced after reaction with water molecules because Cl in the above radical cation is easier to undergo nucleophilic substitution reaction compared to other moieties [3]. Then, RNS attack the C8H15N5O

ro of

with the electron-rich moieties to form hydroxyatrazine (OAIT, Scheme 1). The second route involves attack at the side chain of ATZ. RNS, especially NO•, are likely to react

with ethylamino group or propionylamino group, which leads to subsequent generation

-p

of DEA (m/z = 188.069) or DIA (m/z = 174.054) with the involvement of O2-induced oxidation (Scheme 2). The third route was a dichlorination process which could be

re

ascribed to cleavage of the C-Cl bond because of the direct UV photolysis of ATZ

lP

generating EIT and AIT [51]. Among the aforementioned products, OEIT (m/z = 198.185) has the highest intensity and its intensity increased dramatically in the initial 10 min and gradually decreased (Figure 6A). The other three compounds (DEA, DIA,

na

AIT) showed similar trends with OEIT. Notably, the intensity of OAIT increased continuously with UV fluence, further suggesting the first route made the main

ur

contribution to ATZ degradation.

Jo

Besides, even though the concentration of detected products decreased with the reaction time, the variation of acute toxicity of treated ATZ solution is unclear because of the potential formation of undetected products (e.g. nitrated compounds). Therefore, vibrio fischeri was used to monitor the toxicity variation during the treatment, and results were presented in Fig. S9. As shown, in the first 20 min, the acute toxicity kept decreasing, possibly due to the decreasing concentrations of ATZ and its primary

products (e.g. DEA, DIA, AIT, and OEIT). In the latter phase of ATZ degradation in UV/nitrate system (30-120 min), the acute toxicity of treated solution increased with the reaction time, indicating that further products (e.g. nitrated products) with higher toxicity were generated and accumulated in the solution. The results suggested that further ameliorations are needed for UV/nitrate system to reduce the toxicity of contaminants. 4. Conclusions

ro of

RNS generated from nitrate photolysis have demonstrated capability of degrading

refractory contaminants under optimized operation conditions. Considering the possible application in natural water bodies, the radiation wavelength would be a key

-p

factor. This study demonstrated that the role of RNS in the degradation of contaminants

re

with weakly electron-donating moieties (e.g. ATZ) was dependent on the radiation wavelength.

lP

(1) The radiation wavelength had important influence on ATZ degradation: ATZ could be removed efficiently in UV285/nitrate system (87.7% of removal efficiency at

na

864 mJ cm-2 UV fluence) and inefficiently in UV255/nitrate system (35.2% of removal efficiency at 864 mJ cm-2 UV exposure).

ur

(2) The reactive nitrogen species made the main contribution to ATZ degradation in the

Jo

UV285/nitrate system. The ATZ removal mainly relied on the initial concentration of nitrate according to the variance decomposition analysis.

(3) The environmental factors such as NOM, pH and carbonate/bicarbonate significantly affected the kinetics of ATZ removal in UV/nitrate system.

Declaration of interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Author Contribution Statement Lingjun Bu: Conceptualization; Data curation; Software; Validation; Writing - original

Ningyuan Zhu: Conceptualization; Writing - original draft. Chunquan Li: Investigation; Visualization.

-p

Ying Huang: Conceptualization.

ro of

draft.

Minghao Kong: Formal analysis; Writing - review & editing.

re

Xiaodi Duan: Methodology; Project administration; Supervision; Writing - review & editing.

na

lP

Dionysios D. Dionysiou: Funding acquisition; Writing - review & editing.

ur

Acknowledgments

Jo

This work was supported by the National Natural Science Foundation of China (31772396). N. Zhu also acknowledgements the support from the UCAS Joint PhD Training Program. D. D. Dionysiou also acknowledges support from the University of Cincinnati through a UNESCO co-Chair Professor position on “Water Access and Sustainability” and the Herman Schneider Professorship in the College of Engineering and Applied Sciences.

References [1] S. Gligorovski, R. Strekowski, S. Barbati, D. Vione, Environmental Implications of Hydroxyl Radicals ((*)OH), Chem Rev, 115 (2015) 13051-13092. [2] D. Vione, B. Sur, B.K. Dutta, V. Maurino, C. Minero, On the effect of 2-propanol on phenol photonitration upon nitrate photolysis, Journal of Photochemistry and Photobiology A: Chemistry, 224 (2011) 68-70.

ro of

[3] Y. Huang, M. Kong, D. Westerman, E.G. Xu, S. Coffin, K.H. Cochran, Y. Liu, S.D. Richardson, D. Schlenk, D.D. Dionysiou, Effects of HCO3– on Degradation of

Toxic Contaminants of Emerging Concern by UV/NO3–, Environmental Science

-p

& Technology, 52 (2018) 12697-12707.

re

[4] J. Ge, D. Huang, Z. Han, X. Wang, X. Wang, Z. Wang, Photochemical behavior of benzophenone sunscreens induced by nitrate in aquatic environments, Water Res,

lP

153 (2019) 178-186.

[5] R.C. Scholes, C. Prasse, D.L. Sedlak, The Role of Reactive Nitrogen Species in

na

Sensitized Photolysis of Wastewater-Derived Trace Organic Contaminants, Environ Sci Technol, 53 (2019) 6483-6491.

ur

[6] O. Svoboda, P. Slavicek, Is Nitrate Anion Photodissociation Mediated by Singlet-

Jo

Triplet Absorption?, J Phys Chem Lett, 5 (2014) 1958-1962. [7] S. Goldstein, J. Rabani, Mechanism of Nitrite Formation by Nitrate Photolysis in Aqueous Solutions:  The Role of Peroxynitrite, Nitrogen Dioxide, and Hydroxyl Radical, Journal of the American Chemical Society, 129 (2007) 10597-10601. [8] G. Mark, H.-G. Korth, H.-P. Schuchmann, C. von Sonntag, The photochemistry of

aqueous nitrate ion revisited, Journal of Photochemistry and Photobiology A: Chemistry, 101 (1996) 89-103. [9] K.B. Benedict, A.S. McFall, C. Anastasio, Quantum Yield of Nitrite from the Photolysis of Aqueous Nitrate above 300 nm, Environ Sci Technol, 51 (2017) 4387-4395. [10] H.O. Tugaoen, S. Garcia-Segura, K. Hristovski, P. Westerhoff, Challenges in

ro of

photocatalytic reduction of nitrate as a water treatment technology, Sci Total Environ, 599-600 (2017) 1524-1551.

[11] L. Chu, C. Anastasio, Quantum Yields of Hydroxyl Radical and Nitrogen Dioxide

-p

from the Photolysis of Nitrate on Ice, The Journal of Physical Chemistry A, 107

re

(2003) 9594-9602.

[12] G.V. Buxton, C.L. Greenstock, W.P. Helman, A.B. Ross, Critical review of rate

in aqueous solution, Journal of Physical and Chemical

na

radicals (.OH/.O-)

lP

constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl

Reference Data, 17 (1988) 513-886.

ur

[13] P.L. Brezonik, J. Fulkerson-Brekken, Nitrate-Induced Photolysis in Natural Waters:  Controls on Concentrations of Hydroxyl Radical Photo-Intermediates by

Jo

Natural Scavenging Agents, Environmental Science & Technology, 32 (1998) 3004-3010.

[14] P. Neta, R.E. Huie, A.B. Ross, Rate constants for reactions of inorganic radicals in aqueous solution, J. Phys. Chem. Ref. Data, 17 (1988) 1027-1284. [15] L. Bu, J. Sun, Y. Wu, W. Zhang, X. Duan, S. Zhou, D.D. Dionysiou, J.C. Crittenden,

Non-negligible risk of chloropicrin formation during chlorination with the UV/persulfate pretreatment process in the presence of low concentrations of nitrite, Water Research, 168 (2020) 115194. [16] S. Komtchou, A. Dirany, P. Drogui, D. Robert, P. Lafrance, Removal of atrazine and its by-products from water using electrochemical advanced oxidation processes, Water Research, 125 (2017) 91-103.

ro of

[17] D. Wang, H. Xu, J. Ma, S. Giannakis, X. Lu, H. Chi, S. Song, J. Qi, Enhanced

mineralization of atrazine by surface induced hydroxyl radicals over light-weight granular mixed-quartz sands with ozone, Water Research, 149 (2019) 136-148.

-p

[18] G. Marchetti, M. Minella, V. Maurino, C. Minero, D. Vione, Photochemical

re

transformation of atrazine and formation of photointermediates under conditions

47 (2013) 6211-6222.

lP

relevant to sunlit surface waters: laboratory measures and modelling, Water Res,

na

[19] A. Torrents, B.G. Anderson, S. Bilboulian, W.E. Johnson, C.J. Hapeman, Atrazine Photolysis:  Mechanistic Investigations of Direct and Nitrate-Mediated Hydroxy

ur

Radical Processes and the Influence of Dissolved Organic Carbon from the Chesapeake Bay, Environmental Science & Technology, 31 (1997) 1476-1482.

Jo

[20] M.G. Rhoades, J.L. Meza, C.L. Beseler, P.J. Shea, A. Kahle, J.M. Vose, K.M. Eskridge, R.F. Spalding, Atrazine and nitrate in public drinking water supplies and non-hodgkin lymphoma in nebraska, USA, Environ Health Insights, 7 (2013) 1527. [21] B. Hassanpour, L.D. Geohring, A.R. Klein, S. Giri, L. Aristilde, T.S. Steenhuis,

Application of denitrifying bioreactors for the removal of atrazine in agricultural drainage water, Journal of Environmental Management, 239 (2019) 48-56. [22] X. Duan, T. Sanan, A. de la Cruz, X. He, M. Kong, D.D. Dionysiou, Susceptibility of the Algal Toxin Microcystin-LR to UV/Chlorine Process: Comparison with Chlorination, Environmental Science & Technology, 52 (2018) 8252-8262. [23] X. Xu, B. Gao, X. Tan, X. Zhang, Q. Yue, Y. Wang, Q. Li, Nitrate adsorption by

ro of

stratified wheat straw resin in lab-scale columns, Chemical Engineering Journal, 226 (2013) 1-6.

[24] Q.-H. Wang, L.-J. Yu, Y. Liu, L. Lin, R.-g. Lu, J.-p. Zhu, L. He, Z.-L. Lu, Methods

-p

for the detection and determination of nitrite and nitrate: A review, Talanta, 165

re

(2017) 709-720.

[25] N. Zhu, Y. Wu, J. Tang, P. Duan, L. Yao, E.R. Rene, P.K. Wong, T. An, D.D.

lP

Dionysiou, A New Concept of Promoting Nitrate Reduction in Surface Waters:

na

Simultaneous Supplement of Denitrifiers, Electron Donor Pool and Electron Mediators, Environmental Science & Technology, 52 (2018) 8617-8626.

ur

[26] M. Kwon, Y. Yoon, S. Kim, Y. Jung, T.-M. Hwang, J.-W. Kang, Removal of sulfamethoxazole, ibuprofen and nitrobenzene by UV and UV/chlorine processes:

Jo

A comparative evaluation of 275 nm LED-UV and 254 nm LP-UV, Science of The Total Environment, 637-638 (2018) 1351-1357.

[27] P. Warneck, C. Wurzinger, Product quantum yields for the 305-nm photodecomposition of nitrate in aqueous solution, The Journal of Physical Chemistry, 92 (1988) 6278-6283.

[28] R. Zellner, M. Exner, H. Herrmann, Absolute of quantum yields in the laser photolysis of nitrate, nitrite and dissolved H2O2 at 308 and 351 nm in the temperature range 278-353 K, Journal of Atmospheric Chemistry, 10 (1990) 411425. [29] S. Cheng, X. Zhang, X. Yang, C. Shang, W. Song, J. Fang, Y. Pan, The Multiple Role of Bromide Ion in PPCPs Degradation under UV/Chlorine Treatment,

ro of

Environmental Science & Technology, 52 (2018) 1806-1816.

[30] Z. Wu, J. Fang, Y. Xiang, C. Shang, X. Li, F. Meng, X. Yang, Roles of reactive

chlorine species in trimethoprim degradation in the UV/chlorine process: Kinetics

-p

and transformation pathways, Water Research, 104 (2016) 272-282.

re

[31] I.K. Konstantinou, A.K. Zarkadis, T.A. Albanis, Photodegradation of selected herbicides in various natural waters and soils under environmental conditions,

lP

Journal of Environmental Quality, 30 (2001) 121-130.

na

[32] H. Prosen, L. Zupančič-Kralj, Evaluation of photolysis and hydrolysis of atrazine and its first degradation products in the presence of humic acids, Environmental

ur

Pollution, 133 (2005) 517-529. [33] Y. Huang, C. Han, Y. Liu, M.N. Nadagouda, L. Machala, K.E. O’Shea, V.K.

Jo

Sharma, D.D. Dionysiou, Degradation of atrazine by ZnxCu1−xFe2O4 nanomaterial-catalyzed sulfite under UV–vis light irradiation: Green strategy to generate SO4−, Applied Catalysis B: Environmental, 221 (2018) 380-392.

[34] C. Li, Y. Huang, X. Dong, Z. Sun, X. Duan, B. Ren, S. Zheng, D.D. Dionysiou, Highly efficient activation of peroxymonosulfate by natural negatively-charged

kaolinite with abundant hydroxyl groups for the degradation of atrazine, Applied Catalysis B: Environmental, 247 (2019) 10-23. [35] L.J. Bu, S.M. Zhu, S.Q. Zhou, Degradation of atrazine by electrochemically activated persulfate using BDD anode: Role of radicals and influencing factors, Chemosphere, 195 (2018) 236-244. [36] L. Xia, G. Hoermann, L. Ma, L. Yang, Reducing nitrogen and phosphorus losses

ro of

from arable slope land with contour hedgerows and perennial alfalfa mulching in Three Gorges Area, China, CATENA, 110 (2013) 86-94.

[37] M. Brienza, R. Manasfi, S. Chiron, Relevance of N-nitrosation reactions for

-p

secondary amines in nitrate-rich wastewater under UV-C treatment, Water

re

Research, 162 (2019) 22-29.

[38] L. Bu, J. Ding, N. Zhu, M. Kong, Y. Wu, Z. Shi, S. Zhou, D.D. Dionysiou,

lP

Unraveling different mechanisms of persulfate activation by graphite felt anode

na

and cathode to destruct contaminants of emerging concern, Applied Catalysis B: Environmental, 253 (2019) 140-148.

ur

[39] X. Dong, B. Ren, Z. Sun, C. Li, X. Zhang, M. Kong, S. Zheng, D.D. Dionysiou, Monodispersed CuFe2O4 nanoparticles anchored on natural kaolinite as highly

Jo

efficient peroxymonosulfate catalyst for bisphenol A degradation, Applied Catalysis B: Environmental, 253 (2019) 206-217.

[40] L.R. Bennedsen, In situ chemical oxidation: The mechanisms and applications of chemical oxidants for remediation purposes in: E.G. Søgaard (Ed.) Chemistry of Advanced Environmental Purification Processes of Water, Elsevier, Amsterdam,

2014, pp. 13-74. [41] L. Varanasi, E. Coscarelli, M. Khaksari, L.R. Mazzoleni, D. Minakata, Transformations of dissolved organic matter induced by UV photolysis, Hydroxyl radicals, chlorine radicals, and sulfate radicals in aqueous-phase UV-Based advanced oxidation processes, Water Research, 135 (2018) 22-30. [42] M. Cheng, G. Zeng, D. Huang, C. Lai, P. Xu, C. Zhang, Y. Liu, Hydroxyl radicals

ro of

based advanced oxidation processes (AOPs) for remediation of soils contaminated

with organic compounds: A review, Chemical Engineering Journal, 284 (2016) 582-598.

-p

[43] M. O'Connor, S.R. Helal, D.E. Latch, W.A. Arnold, Quantifying photo-production

Research, 156 (2019) 23-33.

re

of triplet excited states and singlet oxygen from effluent organic matter, Water

lP

[44] S.L. Rosado-Lausell, H. Wang, L. Gutiérrez, O.C. Romero-Maraccini, X.-Z. Niu,

na

K.Y.H. Gin, J.-P. Croué, T.H. Nguyen, Roles of singlet oxygen and triplet excited state of dissolved organic matter formed by different organic matters in

ur

bacteriophage MS2 inactivation, Water Research, 47 (2013) 4869-4879. [45] C.A. Aggelopoulos, D. Tataraki, G. Rassias, Degradation of atrazine in soil by

Jo

dielectric barrier discharge plasma – Potential singlet oxygen mediation, Chemical Engineering Journal, 347 (2018) 682-694.

[46] N.K. Scharko, A.E. Berke, J.D. Raff, Release of Nitrous Acid and Nitrogen Dioxide from Nitrate Photolysis in Acidic Aqueous Solutions, Environmental Science & Technology, 48 (2014) 11991-12001.

[47] F. He, W. Zhao, L. Liang, B. Gu, Photochemical Oxidation of Dissolved Elemental Mercury by Carbonate Radicals in Water, Environmental Science & Technology Letters, 1 (2014) 499-503. [48] S. Yan, Y. Liu, L. Lian, R. Li, J. Ma, H. Zhou, W. Song, Photochemical formation of carbonate radical and its reaction with dissolved organic matters, Water Research, 161 (2019) 288-296.

ro of

[49] S. Goldstein, J. Lind, G. Merényi, Chemistry of Peroxynitrites as Compared to Peroxynitrates, Chemical Reviews, 105 (2005) 2457-2470.

[50] Y. Ji, C. Dong, D. Kong, J. Lu, New insights into atrazine degradation by cobalt

-p

catalyzed peroxymonosulfate oxidation: Kinetics, reaction products and

re

transformation mechanisms, Journal of Hazardous Materials, 285 (2015) 491-500. [51] J.A. Khan, X. He, N.S. Shah, H.M. Khan, E. Hapeshi, D. Fatta-Kassinos, D.D.

lP

Dionysiou, Kinetic and mechanism investigation on the photochemical

na

degradation of atrazine with activated H2O2, S2O82− and HSO5−, Chemical

Jo

ur

Engineering Journal, 252 (2014) 393-403.

1.0

A

Ct/C0

0.8

0.6

0.4

UV255 UV285 UV365

0.2

0.0

0

20

40

60

80

100

120

Time (min) 1.0

ro of

B

0.6

-p

Ct/C0

0.8

0.2

0.0

UV255 UV285

0

150

re

0.4

300

450

600

750

900

-2

lP

UV Fluence (mJ cm )

Figure 1 A) Degradation of ATZ vs. time at different wavelengths in the presence of

Jo

ur

nitrate.

na

nitrate; B) degradation of ATZ vs. UV fluence at UV255 and UV285 in the presence of

A 100 UV Photolysis OH. RNS

Removal (%)

80

60

40

20

0 000 0 0 0 0 200

0

400

0

600

800

UV fluence (mJ cm-2)

B 100

60

40

-p

Removal (%)

80

ro of

UV Photolysis OH. RNS

0 0

200

re

20

400

600

800

-2

C 100

60

RNS OH. UV Photolysis

na

Contribution (%)

80

lP

UV fluence (mJ cm )

ur

40

20

Jo

0

UV255

UV285

Figure 2 A) The removal of atrazine vs. UV fluence by direct UV photolysis, RNS and HO• at UV255/nitrate system; B) The removal of atrazine vs. UV fluence by direct UV photolysis, RNS and HO• at UV285/nitrate system; and C) The contribution (%) of direct UV photolysis, RNS and HO• on atrazine removal for UV255/nitrate and UV285/nitrate, respectively, at 864 mJ cm-2.

A

ro of

B

Jo

ur

na

lP

re

-p

Figure 3 The variance decomposition analysis (VPA) for atrazine degradation in real water under UV255 (A) and UV285 (B).

0.0024

0.0012

UV255

UV255

D

NOM = 0 NOM = 1 mg-C L-1 NOM = 2 mg-C L-1 NOM = 4 mg-C L-1 NOM = 7 mg-C L-1 NOM = 10 mg-C L-1

0.0012

0.0006

(bi)carbonate = 0 (bi)carbonate = 50 mg L-1 (bi)carbonate = 100 mg L-1 (bi)carbonate = 150 mg L-1 (bi)carbonate = 200 mg L-1

0.0018

0.0012

0.0006

0.0000

0.0000

UV255

UV285

0.0030

0.0024

k obs(mJ-1 cm2)

kobs (mJ-1 cm2)

UV285

0.0030

0.0018

0.0012

0.0000

0.0000

0.0024

0.0018

pH = 4.0 pH = 6.1 pH = 7.2 pH = 8.1 pH = 9.0

0.0006

0.0006

C

0.0030

ro of

0.0018

0.2 mM nitrate 2 mM nitrate 4 mM nitrate 6 mM nitrate 10 mM nitrate

UV285

-p

0.0024

k obs(mJ-1 cm2)

B

0.0030

k obs(mJ-1 cm2)

A

UV255

UV285

re

Figure 4 The influence of operation parameters in ATZ removal represented by observed reaction rate constants based on UV fluence: A) the initial concentration of

Jo

ur

na

lP

nitrate; B) the initial pH; C) the presence of NOM; and D) alkalinity.

-p

ro of

h

Jo

ur

na

lP

re

Figure 5 Probable degradation pathways of atrazine in UV285/nitrate system.

6.0E6

A

OEIT m/z = 198.1349

Volume

4.0E6

0.0

0

20

40

60

80

100

Time (min)

4E5

140

re

3E5

2E5

DEA m/z = 188.0697 DIA m/z = 174.0541 OAIT m/z = 170.1036 AIT m/z = 154.1087

lP

Volume

120

-p

5E5

ro of

2.0E6

1E5

na

0

ur

0

20

40

60

80

100

120

140

Time (min)

Figure. 6 Evolution profiles of transformation products of ATZ in the UV285/nitrate

Jo

process. A) OEIT and B) DEA, DIA, OAIT, and AIT.

Table 1 Data used to calculate contributions from UV photolysis, HO•, and RNS to the degradation of ATZ in the UV255/nitrate and UV285/nitrate system. [ATZ]0 = 1 µM, [nitrate]0 = 4 mM, pH = 7.2. 𝒌𝒑𝒉𝒐𝒕𝒐𝒍𝒚𝒔𝒊𝒔

Time Ct/C0 (s)

R

𝒊

𝒕𝒊

× ∫ [𝑨𝑻𝒁]𝒅𝒕

𝐤 𝐇𝐎•

photolysis

× ∫ [𝑨𝑻𝒁]𝒅𝒕

R HO•

R RNS

𝒕𝒊−𝟏

𝒕𝒊−𝟏

1.00

167

0.99

0.0005

0.0005

0.0018

0.0018

0.0036

333

0.98

0.0005

0.0010

0.0018

0.0036

0.0122

UV

1000

0.97

0.0019

0.0029

0.0071

0.0107

0.0191

255

2000

0.92

0.0029

0.0058

0.0105

0.0212

0.0494

4000

0.88

0.0055

0.0113

0.0203

0.0415

0.0700

8000

0.83

0.0103

0.0217

0.0379

0.0794

0.0720

16000

0.74

0.0178

0.0653

0.1447

0.0745

0

1.00

300

0.92

UV

600

0.84

285

1800

Jo

7200

-p

re

lP

0.0395

0.0081

0.0006

0.0006

0.0676

0.0078

0.0160

0.0006

0.0013

0.1461

na

0.0081

0.61

0.0287

0.0447

0.0023

0.0036

0.3380

0.41

0.0349

0.0796

0.0028

0.0064

0.5068

0.0407

0.1203

0.0033

0.0096

0.7300

ur

3600

ro of

0

0.14